On the need for a global engineering initiative to mitigate climate change

There is growing scientific evidence that the continued emission of greenhouse gases will eventually lead to catastrophic irreversible climate change and that, therefore, a global effort needs to be started to transition to a fully renewable economy. In this article, the engineering challenges of converting to emission-free power generation are reviewed and the feasibility of two proposed solutions, i.e. the ‘wind–water–solar’ and the ‘energy ship’ proposals, are discussed. It is concluded that a well-conceived and executed engineering effort needs to be initiated and guided by a Global Engineering Council for the purpose of examining and ranking various proposals and making specific recommendations

A general method for unsteady stagnation region heat transfer and results for model turbine flows

Recent experiments suggest that the heat-transfer characteristics of stator blades are influenced by the frequency of passing of upstream rotor blades. The calculation of these effects requires that the movement of the stagnation point with variations in freestream velocity is properly represented together with the possible effects of turbulence characteristics on the thin leading-edge boundary layer. A procedure to permit the achievement of these purposes is described for laminar flows in this paper together with results of its application to two model problems which demonstrate its abilities and quantify the influence of wake characteristics on fluid-dynamic and heat-transfer properties of the flow and their effects on surface heat transfer

Optimal energy systems design applied to an innovative ocean–wind energy converter

System level optimization is used to design an innovative ocean–wind energy converter to meet the “as good as it can be done” design objective. This general design procedure is then applied to the design of a 20 kW energy system and it is demonstrated that a combined energetic and economical design procedure is required for an optimal solution

Techno-Economic Comparison of Renewable Energy Systems Using Multi-Pole System Analysis (MPSA)

The recently published method of multi-pole system analysis (MPSA) is used to techno-economically compare two wind-energy converters: offshore wind turbines and the energy ship concept. According to the method, both systems are (i) modeled, (ii) energetically and economically analyzed, (iii) techno- economically optimized and, finally, (iv) expected uncertainties are calculated and assessed. The results of the method are used to derive the necessary cost reduction of the wind-energy converters to be economically competitive to fossil-fuel-based technologies

Aerodynamic Analysis and Design of High-Performance Sails

High-performance sails, such as the ones used on the America Cup boats, require sails whose aerodynamic characteristics approach those of rigid wings, yet permit a reduction in sail area in high wind and sea conditions. To this end, two-cloth sails are coming into use. These sails are constructed out of an articulated forebody that is a truncated ellipse, the aft of which has sail tracks, or rollers, along the edges to accommodate the twin sails. As the sails on either side need to be of the same length, due to the requirement to sail on different tacks, the two cloth sections need to be of equal length. The requirement then is to have their clews separated and able to slide over each other. More importantly, the transition between the rigid mast section and sails needs to be as aerodynamically smooth as possible in order to reduce drag and hence maximize the lift to drag ratio of the airfoil section that is made up of the mast and twin sails. A computational analysis using ANSYS CFX is presented in this chapter which shows that the aerodynamic characteristics of this type of two-cloth sail are almost as good as those of two-element rigid wing sections. Optimum sail trim configurations are analyzed in order to maximize the thrust production. Applications may soon extend beyond competitive sailing purposes for use on sailing ships equipped with hydrokinetic turbines to produce hydrogen via electrolysis (energy ships). Additionally, high performance sails can be used onboard cargo ships to reduce overall fuel consumption

Steady and stall analysis of the NLR 7301 airfoil

The static and dynamic stall behavior of the supercritical NLR 7301 airfoil is analyzed with a 2D thin-layer Navier-Stokes code. The code solves the compressible Reynolds-averaged Navier-Stokes equations with an upwind biased numerical scheme in combination with the Baldwin-Lomax or the Baldwin-Barth turbulence models. The effect of boundary layer transition is incorporated using the transition length model of Gostelow et al. The transition onset location is determined with Michel's formula or it can be specified as an input parameter. The two turbulence models yield significantly different steady-state lift coefficients at incidences greater than 8 degrees. Also, the lift hysteresis loops are strongly affected by the choice of the turbulence model. The use of the one-equation Baldwin-Barth model together with the Gostelow transition model is found to give substantially better agreement with the experimental data of McCroskey et al. than the Baldwin-Lomax model.Deutsche Forshungsgemeinschaft (DFG) and the Naval Postgraduate Schoo

A Navier-Stokes analysis of the stall flutter characteristics of the Buffum cascade

Numerical stall flutter prediction methods are much needed, as modern jet engines require blade designs close to the stability boundaries of the performance map. A Quasi-3D Navier–Stokes code is used to analyze the flow over the oscillating cascade designed and manufactured by Pratt & Whitney, and studied at the NASA Glenn Research Center by Buffum et al. The numerical method solves for the governing equations with a fully implicit time-marching technique in a single passage by making use of a direct-store, periodic boundary condition. For turbulence modeling, the Baldwin–Lomax model is used. To account for transition, the criterion to predict the onset location suggested by Baldwin and Lomax is incorporated. Buffum et al. investigated two incidence cases for three different Mach numbers. The low-incidence case at a Mach number of 0.5 exhibited the formation of small separation bubbles at reduced oscillation frequencies of 0.8 and 1.2. For this case the present approach yielded good agreement with the steady and oscillatory measurements. At high incidence at the same Mach number of 0.5 the measured steady-state pressure distribution and the separation bubble on the upper surface was also found in good agreement with the experiment. But computations for oscillations at high incidence failed to predict the negative damping contribution caused by the leading edge separation.Deutsche Forshungsgemeinschaft (DFG)Naval Postgraduate Schoo

Computational prediction of airfoil dynamic stall

The term dynamic stall refers to unsteady flow separation occurring on aerodynamic bodies, such as airfoils and wings, which execute an unsteady motion. The prediction of dynamic stall is important for flight vehicle, turbomachinery, and wind turbine applications. Due to the complicated flow physics of the dynamic stall phenomenon the industry has been forced to use empirical methods for its prediction. However, recent progress in computational methods and the tremendous increase in computing power has made possible the use of the full fluid dynamic governing equations for dynamic stall investigation and prediction in the design process. It is the objective of this review to present the major approaches and results obtained in recent years and to point out existing deficiencies and possibilities for improvements. To this end, potential flow, boundary layer, viscous-inviscid interaction, and Navier-Stokes methods are described. The most commonly used numerical schemes for their solution are briefly described. Turbulence models used for the computation of high Reynolds number turbulent flows, which are of primary interest to industry, are presented. The impact of transition from laminar to turbulent flow on the dynamic stall phenonmenon is discussed and currently available methods for it prediction are summarized. The main computational results obtained for airfoil and wing dynamic stall and comparisons with available experimental measurements are present. The review concludes with a discussion of existing deficiencies and possiblities for future improvements

Ocean Wind Power: Is it the key for a rapid transition to renewable energy? [video]

NPS Defense Energy SeminarIn his lecture Dr. Platzer will argue that the time has come to develop innovative engineering solutions to reduce the global carbon dioxide emissions in order to avert irreversible climate change. He will first present the empirical evidence for global climate change and draw attention to the fact that the available global wind resources are quite sufficient to combat climate change if the winds over the oceans are exploited for power generation. He will show how large unmanned autonomously operating sailing ships can be used to convert the ocean wind power into hydrogen in order to convert the global fossil-based economy into a global hydrogen-based economy. He will conclude with an assessment of recent initiatives to combat climate change. In particular, he will draw attention to the recent call for a Global Apollo Program

A Computational Study on the Dynamic Stall of a Flapping Airfoil

The article of record as published may be found at http://dx.doi.org/10.2514/6.1998-2519The dynamic stall boundaries of a NACA 0012 airfoil oscillating in either the pure plunge mode or in the combined pitch and plunge mode is computed using a thin-layer Navier-Stokes solver. Unsteady flowfields are computed at the free-stream Mach number of 0.3, the Reynolds number of 1 • 106, and the Baldwin-Lomax turbulence model is employed. It is found that the pure plunge oscillation leads to dynamic stall as soon as the non-dimensional plunge velocity exceeds the approximate value of 0.35. In addition, the power extraction capability of the airfoil operating in the wingmill mode is studied by computing the dynamic stall boundary for a combined pitch and plunge motion at the reduced frequency values of 0.1, 0.25 and 0.5.Naval Research LaboratoryNaval Research Laborator